There was never a version of this game with speech. The 2015 GOG release includes the original DOS version in EGA and also the 1991 FM Towns version with VGA graphics and “higher-quality music and sound effects”.

If I remember correctly, the first LucasArts games with full voice overs were released in 1993 - Day of the Tentacle, Sam & Max Hit the Road, and also Indiana Jones and the Fate of Atlantis.

The only LucasArts FM Towns release supporting voice was Indiana Jones and the Fate of Atlantis.

Perhaps it is just a misunderstanding based on the fact that the original LucasArts FM Towns games were released on CD media, and around the same time LucasArts began porting its adventure games to CD-ROM as talkies for PC. So for those unfamiliar with the history of FM Towns, it might lead to confusion, expecting that the FM Towns games would be talkies like their PC equivalents.

And yes, I know there are some exceptions, like the PC CD release of Monkey Island 1 with enhanced music but no voice, and the above mentioned Fate of Atlantis for FM Towns with voice.